A typical television broadcast station transmits video signals in standard resolution. When the video signals are received by a video signal receiver, the standard resolution is expanded if the resolution of the display associated with the video signal receiver is higher than the standard resolution, compressed if the resolution of the display is less than the standard resolution, or left unchanged if the resolution of the display is the same as the standard resolution. A conventional video signal receiver includes a main-channel format converter (MFC) for expanding or compressing the resolution of the received video signal. The MFC includes a horizontal format converter (HFC) for performing resolution conversion in the horizontal direction and a vertical format converter (VFC) for performing resolution conversion in the vertical direction.
Referring now to FIG. 1, a conventional HFC 10 is shown. HFC 10 includes, inter alia, a circular or FIFO buffer 12, processing circuitry 16, a HFC filter 18, and a HFC controller 14. In operation, an incoming video stream is buffered in FIFO buffer 12. The video stream consists of a series of frames. Each frame contains a series of lines, and each of the lines contains a plurality of pixels. Detection circuitry (not shown) detects the resolution of the incoming video stream, compares the detected resolution to the known resolution of the associated display, and transmits an appropriate zoom ratio signal to HFC controller 14. The zoom ratio is an expansion or compression ratio that may be expressed as follows:Zoom ratio=(output data size)/(input data size)Thus, if the zoom ratio is greater than 1, expansion of the input data (i.e., expansion of the horizontal pixel line buffered in FIFO buffer 12) is necessary. If the zoom ratio is less than 1, compression of the input data (i.e., compression of the horizontal pixel line buffered in FIFO buffer 12) is necessary. If the zoom ratio is equal to 1, neither compression nor expansion of the input data is necessary.
For example, if the zoom ratio is 1/3 then HFC filter 18 requires three input pixels to generate an output pixel. Thus, a fixed sequence of input pixels (3, 3, 3. . . ) is necessary to generate the desired output pixels. If the zoom ratio is 4/10 then HFC filter requires ten input pixels to generate four output pixels. This is achieved by deriving the first output pixel from the first three input pixels, the second output pixel from the next two input pixels, the third output pixel from the next three input pixels, and the fourth output pixel from the final two input pixels. Thus, a variable sequence of input pixels (3, 2, 3, 2. . . ) is necessary to generate the desired output pixels.
In conventional HFC 10, FIFO buffer 12 has a fixed data size. In other words, FIFO buffer 12 outputs a fixed sequence of input pixels (e.g., 1, 2, or 3 pixels) in response to a read request from HFC controller 14. If the required number of input pixels is different from the number of input pixels read from FIFO buffer 12, HFC controller 14 configures complicated processing circuitry 16 to provide HFC filter 18 with the necessary sequence of input pixels required to permit HFC filter 18 to generate the desired output pixels. The utilization of the processing circuitry 16 suffers from a number of drawbacks. One drawback is that processing circuitry 16 requires multiple clock cycles to generate a variable pixel sequence from the fixed output FIFO buffer 12 and, thus, slows the throughput of HFC 10. Another drawback is that processing circuitry 16 uses up expensive real estate on an integrated circuit that might otherwise be utilized for other critical functions.
The present invention is directed to overcoming the drawbacks discussed above.